1. Field of the Invention
This invention relates to pneumatic radial tires, and more particularly to so-called high-performance pneumatic radial tire having excellent running performances which provides an excellent steering stability on dry road surface and controls noise to a sufficiently low level and effectively improves a drainage property on wet road surface.
2. Description of the Related Art
In the conventional high-performance tire, it is general to adopt so-called directional tread pattern comprising a combination of straight circumferential groove(s) extending in the Circumferential direction of the tire and slant grooves extending substantially in a V-shaped form viewed from a front of the tire. The maintenance of more excellent drainage property in such a tire is frequently attained by enhancing a negative ratio.
On the other hand, it has been confirmed that the drainage property may be improved by using a combination of slant grooves extending substantially in a V-shaped form viewed from the front of the tire and steeply slant grooves extending in the same direction of the above slant grooves and having particularly a small inclination angle with respect to a pattern center, and arranging gently slant grooves in a side region of the tread for the drainage toward the side of the tire.
In the above conventional techniques, the straight circumferential groove and the slant groove or the slant groove and the steeply slant groove are crossed with each other in the formation of the tread pattern, so that when water existing on a road surface is drained through each groove during the running of the tire under a load, disorder of water flow resulted from the joining at a joint position and disorder of water flow resulted from the large change of water flow at a divergent position are created, respectively, which undesirably bring about the lowering of the drainage efficiency.